Residual Stress Evaluation in TiN Coatings Used for Erosion Protection of Aerospace Components

A laser beam profilometry technique was used to investigate residual stress accumulation during TiN deposition and stress relaxation during post-deposition heat treatment. The test coatings were reactively sputtered on silicon and steel substrates using a UMS technique. TiN coatings, deposited at different bias and pressure levels, were evaluated for residual stress and microhardness. It was found that both the residual stress and the hardness were strongly affected by the coating deposition conditions. In addition, stress-temperature correlations were obtained by subjecting the coatings to temperature cycles up to 450°C. Stress-temperature plots revealed that the level of residual stress relaxation depended on deposition conditions and only coatings deposited at low ion bombardment could be fully annealed. The role of intrinsic and thermal stresses in the total residual stress in the coating/substrate system was also discussed.